Incandescent electric lamp



RA B. THOMAS Feb. 14, 1939.

INCANDESGRNT ELECTRIC LAMP Filed Nov. 7, 1.938

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A-rToFM/EY- Patented Feb. 14, -1939 UNITED STATES PATENT oFFlcI-z INCANDESCENT ELECTRIC LAIVIP Application November 7, 1938, Serial No. 239,243

10 Claims. (Cl. 176-32) This invention relates to incandescent electric lamps, and particularly to such lamps of the lbipost type, gas-filled.

When the filament of such a lamp burns out,

an electric arc occurs across the break in the filature a fuse which will blow before the lamp current rises to the destructive value. The fuse must be positive in action, and should be placed outside of the sealed glass bulb of the lamp.

Accordingly, one of the objects of the present invention is to incorporate in such a lamp a fuse which will be positive in its action toward preventing destructive arcs.

A further object of the invention is to provide such a fuse in the outwardly extending contact prong at the base.of the lamp.

Another object is to provide proper arcquenching insulation for the fuse and yet keep the prong an integral unit.

Further objects and advantages will be apparent from the following description 4and the accompanying drawing in which:

Figure 1 is a profile view of the finished bipost lamp, and

Figure 2 is an enlarged view, in cross-section, of the fuse and prong of the lamp.

Figure 1 shows a lamp in a glass bulb I, preferably of Pyrex or hard glass. The filament 2, generally arranged in a plane, is supported from the wire leads 3, 3, the insulating pieces 4, 4;

preferably of ceramic or refractory material, and the hooks II. A metal gauze piece 5, may be attached to each lead to collect particles of tungsten evaporated from the filament 2 and carried upward by convection currents in the gas, but the same piece cannot be connected to both leads as it will cause a short circuit. The leads are rigidly attached to the base prongs 'I, l, the whole forming a rigid assembly. The base prongs are preferably surrounded by .the thin metal cups 8, 8, of a metal, such as Fernico, which is capable of being sealed to the glass used. A bushing, or sealing ring of copper 9, 9, is generally used between the prong l, and the cup 8, the bushing being generally formed by a brazing process. The fuse is contained in the prong 1, and is shown in more detail in Figure 2. Preferably, as shown, only one prong has a fuse.

In the latter figure, the metal prong 1, to which the lead 3, is attached, extends in the form of a 5 hollow shaft I2, beyond the cup 8. The fuse wire III, is electrically connected, as by solder 6, to the bottom of this hollow shaft, and extends such distance as is required. An insulating tube I4, which may be conveniently made of glass, is placed around the fuse I0, to insulate it from the hollow shaft of the prong. An insulating material of ceramic I5, or similar material having a slight shoulder on one end, is placed around the outer surface of the hollow shaft I2, and a l5 metal sleeve I6, is placed over it to provide an outer contact for the lamp and to partially close the open end of the metal prong, as by the sleeves being mounted inward at its end. A reasonable distance, for example 11,; inch, should L be allowed between the end of the prong and the lower end of the metal sleeve I6; this distance may be fixed by the dimensions of the shoulder of the ceramic'lnsulator I5. The top of the fuse I0, is connected by a heavy wire I9, of larger di- Q ameter than the fuse wire and of copper or other material of good conductivity to the top of the metal sleeve IS, and the opening at the sleeve is closed by a plug. I'I, of cement I8, which also serves to hold the sleeve and the prong together. This cement may extend down as far as the :fuse I0, if desired.

The cement I8, used in the plug I1, may consist of ziriium silicate of about 150 mesh mixed with enou h sodium silicate to form a fairly dry :xr paste whic will not flow readily, but which may be pushe f into the top of the metal sleeve I 8. The cem nt may be set preferably by heating to a temperature of about 100 C., and will then be somewhat porous, allowing the gases formed by the fuse burnout to diffuse through it. Other suitable cements may, of course, be used if de sired..

I have found a wire consisting of nickel, or of a nickel alloy such as nickel and manganese, to 4,-, be suitable for the fuse wire I0, although other wires may also be used.

The cup 8, of metal, sealed to the glass of the lamp envelope may be of Fernico metal if the glass envelope is made of a hard or high melting point borosilicate glass, such as that commonly known as Pyrex glass. Fernico consists of 54% iron, 28% nickel, and 18% cobalt.

The impossibility of properly protecting the lamp against arcing at burnout has prevented the filling of prior art lamps of the type described, with gases such as pure argon, or 98% I0, does not travel beyond the limits of the fuse Awire itself.

If the fuse wire itself were continued in sumcient length to make contact with the external terminal, the fuse might blow at the outer surface or socketcontact of the metal sleeve I3, and cause an arc which would continue across the socket contacts which are closely spaced at the base. The arc at fuse burnout is conned to the space inside the cemented seal. This cement being porous, temporarily coniines the gases resulting from the vaporization of the fuse material, thereby permitting an abnormal pressure to result which acts to assist in quenching the fuse arc and subsequently permits a retarded diffusion of these gases with resulting slow return to normal pressure within the fuseA chamber.

What I claim is: v

l. In a lamp of the character described, a base contact pron vent destruc ive arcing at burnout of the lamp.

2. In a gas-filled electric incandescent lamp, a glass envelope, a lament supported by rigid leads attached to external contact prongs sealed through said glass envelope and extending outwardly therefrom, said contact prong containing an internal fuse to prevent destructive arcing at burnout of the lamp. v

'3. In a lamp of the character described, a base contact prong. containing an internal fuse therein, said fuse comprising a fuse wire electrically connected to the bottom of said prong', and an insulating tube enclosing said fuse wire inside of said prong.

4. In a lamp of the character described, a base contact prong bearing an internal fuse, said fuse comprising a fuse wire electrically connected to bottom of said prong, an insulating tube enclosing said fuse wire inside of said prong and a heavy conductive wire connected to the fuse wire and to an external sleeve insulated from said prong.

5. In a lamp of the character described, a base contact prong containing an internal fuse, said fuse comprising a fuse wire electrically connected to bottom of said prong, an insulating tube enclosing said fuse wire inside of said prong, a wire of larger diameter than the fuse wire and of more conductive material, connected to saidl fuse wirey and to an external sleeve insulated from said prong, and a porous insulating cement sealing the fuse cavity of the prong.

containing an internal fuse to pre- 6. In a lamp of the character described, a base contact prong containing an internal fuse, said fuse comprising a fuse wire electrically connected to bottom of said prong, an insulating tube enclosing said f use wire inside o f said prong. a wire of larger diameter 4than the fuse wire and of more conductive material, connected to said fuse wire and to an external sleeve insulated from said prong, a porous insulating cement sealing the fuse cavity of the prong, an insulating material placed around the outer surface of said prong and a metal sleeve enclosing said insulating material and sealed to said non-fusing conductive wire by said cement.

7. In a lamp of the character described. a base cohtact prong containing an internal fuse, said fuse` comprising a fuse wire electrically connected to bottom of said prong, an insulating tube enclosing said fuse Wire inside of said prong. a wire of larger diameter than the fuse wire and .of more conductive material connected to said fuse wirev and to an external sleeve insulated from said prong, an insulating porous cement I sealing the fuse cavity of said prong, an insulating material placed around the outer surface of said prong. containing a shoulder one-sixteenth of an inch or greater at one end, said shoulder separating the metal of the outer sleeve from the protruded lip of said prong, and a. metal sleeve reentrant on one end enclosing said insulating material and sealed to said non-fusing conductive wire by said semi-porous cement.

8. In an electric incandescent lamp, a glass envelope, a lament supported by two rigid leads attached to external contact prongs sealed to the glass envelope and extending outwardly therefrom, said contact prong comprising a metal extension `in the form of a hollow shaft, a fuse wire inside said hollow shaft and electrically connected to the bottom thereof, an insulating tubev enclosing said fuse Wire and inside said shaft, a wire of larger diameter than the fuse wire and of more conductive material, and attached to end of the fuse not connected to bottom of said shaft, an insulating material around the outer surface of said hollow shaft, a metal sleeve wire and attached to the end of the fuse wire is of copper.

l0. In a lamp of the character described, a sealed glass envelope, a tungsten filament within said envelope, and connected to base prongs sealed through and extending outwardly from said envelope, a fuse inside one ofysaid base prongs, and an atmosphere consisting of at least` 98 per cent pure argon inside said envelope.

RALPH B. THOMAS. 

